THE VISCOSITY OF fVASA'.x 247

f orc*e» then each molecule of gas when it out of the

of t,h^ molecular force of the solid must have the
as when it went In, so that without

of gas and solid there can t>e no of

to the gas. If, then, molecules of gas and
of gas must collide amongst themselves."
I xi the theory of diffusional viscosity explained It

plain that there would be viscous If the

failed to collide with each other entirety.
I£LXX<!*S view is in accordance with the one we as

Ci eollisional viscosity ?J in that collisions

be the nature aad origin of the collisions, an

the viscosity. Sutherland attributes the to

"the* attraction between the molecules, whereas the of
ctiiiski would lead us to ascribe the effect to the of the

molecules. The two points of view are essentially the
Sutherland's theory led him to the formula

oir

1+aC

a is tlie coef5.cie.nt of expansion of a gas C is a
This f ormiila has had the most remarkable of
tia/v^ been, proposed, although it does not apply to
A. single example of its performance is given la the
•fca/ble, using Holman's (1886) data for carbon at
l>tieric pressure.
Ex:amirimg Sutherland's formula, we observe ike
csorxsfcant C is small in comparison with the
-th.e formula reduces to the simple theoretical formula
1? = KT*
Tlio discovery, (cf. Vogel (1914)), that Sutherland's formula
a/fe* low temperatures indicates tkat it does not
account of the deviation from the simple formula.
Quite in harmony with the above> it is found that the